Some enzyme electrodes can obtain a response correlated with the concentration of a ground substance in the manner of current measurement using the redox enzyme. An example thereof is obtained by fixing the redox enzyme to platinized carbon (for example, see Patent Document 1 to 3). The enzyme electrode using the platinized carbon advantageously eliminates the need for an electron mediator.
Enzyme electrodes described in Patent Document 1 to 3 are obtained by immobilizing a redox enzyme to a porous layer formed by bonding a platinized carbon particle using a binder. The platinized carbon particle is obtained by holding platinum on the surface of the carbon particle. Platinum is held on the carbon particle as a metal particle, a platinum oxide particle or an oxide particle obtained by oxidizing the surface of a platinum particle. Glucose oxidase (GOD) is disclosed as the redox enzyme.
The enzyme electrode may be obtained by forming the porous layer as a surface layer on the surface of a conductive supporting member. As the conductive supporting member, carbon paper or a web of a carbon fiber of a filament is used.
In the enzyme electrodes described in Patent Documents 1, 2, a synthetic resin, preferably polytetrafluoroethylene is used as the binder.
On the other hand, in the enzyme electrode described in Patent Document 3, as the binder, there is not used a binder (that is, a high-melting point fluorocarbon resin or a hydrophobic resin, for example, polytetrafluoroethylene) which needs a high temperature for sintering processing but a water-soluble or water dispersible binder, for example, gelatin in order to realize the mass production of the enzyme electrode.
The present inventors have experimentally produced a glucose dehydrogenase (GDH) platinized carbon enzyme electrode using, as a binder, a solid polyelectrolyte used much for an ion-exchange membrane or the like in the field of a fuel cell. There was used NAFION (registered trademark) which was particularly preferable as the solid polyelectrolyte and was developed by Du Pont Company of United States of America. Since NAFION has high endurance and chemical stability, NAFION is a fluorine sulfonic acid polymer electrolyte which is stronger in the operation at a high temperature than of other electrolysis film. Similarly, a paraffin wax as a petroleum wax was used as a binder, and an enzyme electrode was experimentally produced. Neither NAFION nor the paraffin wax needs the sintering of a high temperature.
However, when voltammetric measurement or amperometric measurement was carried out using the GDH platinized carbon enzyme electrode as an anode electrode, and using glucose of an enzyme ground substance as a measuring object, accordingly, the output characteristics of a measurement sensor including the GDH platinized carbon enzyme electrode were different and the reproducibility was low (not stabilized) whenever a measurement sensor was experimentally produced.
Therefore, in a measurement using a voltammetric method or an amperometric method when carrying out glucose measurement using the GDH platinized carbon enzyme electrode, the stable operation may not be able to be carried out as it is, or the operation condition as the enzyme electrode may be mostly limited. As a result, the condition range of the appropriate operation may become very narrow.
Patent Document 1: WO87/No. 07295 pamphlet
Patent Document 2: Japanese Patent Application National Publication (Laid-Open) No. 02-501679
Patent Document 3: Japanese Patent Application Laid-Open (JP-A) No. 02-99849